1. Field of the Invention
This invention relates generally to apparatus and methods for segregation of scrap metal pieces by identification of their individual alloy compositions, and more particularly, to identification of alloy compositions by optical analyses of sparks generated therefrom.
2. Background of the Invention
The science of spectroscopy involves detailed analyses of wavelength spectra characterizing the electromagnetic radiation given off by heated bodies, and it has long been known that heated metal alloys emit such electromagnetic radiation in colors related to the constituent elements in their alloy compositions. When an alloy is sufficiently heated, each constituent element emits visible light primarily at a characteristic wavelength, i.e., has its own visually observable signature. The intensity of the emission from each element, at its characteristic wavelength, is relatable to the proportion in which that element is present in the alloy being examined.
It has also been known for a long time, as indicated by the literature cited below, that the color and shape of the spark pattern given off when a grinding wheel is applied to a metal piece can be related to the metal composition. This is simply because the sparks are really only very small glowing pieces of the metal heated to very high temperatures by the rapid input of mechanical energy from the grinding wheel which tears them off the parent metal piece. The use of this technique has been limited by the availability of skilled individuals, who must rely solely on personal experience and judgment to identify metal alloys by the color and shape of the spark pattern. In the prior art, to date, the utilization of spectral information in metal-grinding sparks has been based on and limited to subjective sensory impressions, which precludes distinguishing among alloys with minor compositional differences.
All of the high-nickel superalloys, for example, are characterized by a short, red spark and cannot be separated using the conventional subjective technique. Such alloys generally are identified by sophisticated laboratory techniques requiring skilled personnel qualified in emission spectroscopy, fluorescent x-ray spectroscopy, or atomic absorption spectroscopy and the like. The apparatus and methods taught in this invention, however, can precisely and easily separate such superalloys into individual alloys, on the basis of relatively subtle spectral differences in the sparks ground off from them.
This invention, therefore, is intended to enable even unskilled persons to easily, rapidly and accurately identify scrap metal pieces by their different alloy compositions, thereby to correctly segregate them for subsequent reprocessing.
Allen et al U.S. Pat. No. 4,269,507 pulverizes solids with a grindstone and injects propelled particles into a flame for analysis by a mass spectrometer. The cone of the mass spectrometer must be placed into the flame to analyze the content of the propelled particles.
In Vreeland U.S. Pat. No. 2,751,811 the spectrum of a sample is compared with a standard spectrogram by heating the sample to incandescence in an electric arc, and exposing the glowing pieces to a spectrograph.
Neither approach is suitable for unskilled personnel outside a laboratory or other controlled environment.